A variety of biological reactors including standard fermenters and specialty bioreactors have been used to produce primary and secondary metabolites from mammalian, plant, and insect cells, bacteria, yeasts, and fungi. As the use of recombinant proteins and other metabolites increases, the demand for efficient and cost effective biological reactors is expected to increase.
The importance of developing an efficient culture perfusion system has been repeatedly addressed in the literature. The most critical element in a culture perfusion system is the cell/medium separator. There are two major classes of techniques for the separation of cells from the medium in perfusion bioreactors, namely, by gravitational or centrifugal sedimentation, and by tangential filtration (e.g. axial rotation filtration such as spin filters or cross flow filtration).
Sato et al. (Journal of Tissue culture Methods. 8: 167-171, 1983), describe an internal conical cell separator consisting of a tapered conical sedimentation chamber affixed to the headplate of a bioreactor. Spent medium is extracted through the top of the cone and cells settle and slide down the steep walls of the cone to the fermenter.
Kitano et al. (Journal of Applied Microbiology and Biotechnology, 24:282-286 1986), describe a modified version of the system developed by Sato et al which uses a conical cell precipitator placed above the bioreactor and connected by tubes to the culture to separate cells from media.
Tyo and Thilly, in their paper presented at the section of New Developments in Mammalian Cell Reactor Studies, Annual Meeting, American Institute of Chemical Engineers (AICHE), 1989, describe a system consisting of a series of nested truncated cones with an innermost solid cone. Cells and medium are pumped up through the cones while cells are collected on the lower surface of the cones, thereby resulting in a virtually cell-free fluid.
The above mentioned designs have the settler inserted directly into the turbulent well-mixed region of the bioreactor and therefore the sedimentation process is vulnerable to disturbance by fluid turbulence. In addition, the entrance into the above settlers is small and therefore clogging can occur.
It is an object of the present invention to provide a perfusion air-lift bioreactor for cultivating microbial, plant, animal or insect cells to produce valuable metabolites in which improved cell/medium separation can be achieved. It is another object of the invention to provide such a reactor in which disturbance to particle sedimentation is minimized.